Speaking to Wheels in Sweden, Rohrl said that testing of the facelifted 991-series 911 is already well underway at Porsche’s Nardo Technical Centre in Italy.

The current Carrera produces 257kW from a 3.6-litre naturally aspirated flat-six, while the Carrera S uses a 3.8-litre version to produce 294kW.

“I’ve driven the new 911 and they will be 2.7, and 3.0 litres in S form,” he said.

“At least it’s not a four-cylinder turbo like in the next Boxster. That sounds like a Volkswagen Beetle, I’m not kidding you! I tell the guys, ‘You’re joking with this sound, right?’ But they just say they are working on it. I’m sure they will get it right.”

Porsche engineering chief Wolfgang Hatz said at the Detroit auto show in January the next Boxster and Cayman will use a four-cylinder turbo.

Rohrl wouldn’t be drawn on how much torque a turbocharged 911 will produce, but we guarantee it’ll be considerably more than the current Carrera’s 390Nm and the Carrera S’s 440Nm.

The need for greater efficiency and fewer emissions is behind Porsche’s move to turbocharging, much to the disappointment of Rohrl.

“We need to go to turbocharging to reduce emissions,” he said. “How else can we get C02 levels below 95g?

“But no matter how good a turbo engine is, it can never have the pure response of a naturally aspirated engine. This is the reason I bought a Boxster Spyder, because engines like this won’t be made anymore.”

Porsche has a long history with 2.7-litre flat-six engines, stretches back to 1973 and the homologation special Carrera RS 2.7. By 1974 all 911s used a 2.7-litre flat six.